Cilybebyll Auxiliary Unit Operational Base

Cadw's description

Summary description and reason for designation

The following provides a general description of the Scheduled Ancient Monument.

The monument comprises the remains of an Auxiliary Unit Operational Base, which dates from the Second World War (1939-45 AD). It is situated 250m east-north-east of Plas Cilybebyll house where its location set below ground in woodland ensured that it was hard to detect. Operational bases were built in the coastal districts along the length of the British coastline where a German invasion was expected. The structure consists of a concrete floor, brick built end walls and entrance shaft, together with a curved corrugated sheet steel roof and side walls resting on low sills. It is aligned north-east by south-west and the entrance is located at the north-east end. Internally the structure consists of a single room that measures 4.25m in length, 3.07m in width and 1.95m in height. The collapsed remains of an escape tunnel lead away from the entrance in the south-west wall.

The monument is of national importance for its potential to enhance our knowledge of the British Auxiliary Unit organisation and the buildings it built and used. Very little is known about this organisation, due to the continuing secrecy surrounding its establishment and the fact that many operational bases were destroyed after the War. While a partial list of operational bases survives for Wales, this is one of very few where the location is known and the structure is in good enough condition to provide details of construction, form and layout. The remains are well preserved and retain significant archaeological potential, with a strong probability of the presence of associated archaeological features.

The area scheduled comprises the remains described and an area around within which related evidence may be expected to survive.